The broad and long-term objectives of this research program are to elucidate the endocrine and neuroendocrine control systems which govern reproductive processes in a representative primate, the rhesus monkey. Specifically, we propose to continue our explorations in the regulation of gonadotropic hormone and prolactin secretion during the menstrual cycle and during lactation with particular emphasis on the role of neural mechanisms. In addition, we shall continue to address the determinants of the functional life-span of the corpus luteum during the normal menstrual cycle, in early and late pregnancy and during lactation. Radioimmunoassays are now available for all the rhesus monkey reproductive hormones (including prolactin) and techniques for the study of hypothalamic function using pharmacological, neurosurgical and neurophysiological approaches are in various stages of development. BIBLIOGRAPHIC REFERENCES: Krey, L.C., W.R. Butler and E. Knobil. Surgical disconnection of the medial basal hypothalamus and pituitary function in the rhesus monkey. I. Gonadotropin secretion. Endocrinology 96:1073, 1975. Krey, L.C., K-H. Lu, W.R. Butler, J. Hotchkiss, F. Piva and E. Knobil. Surgical disconnection of the medial basal hypothalamus and pituitary function in the rhesus monkey. II. Growth hormone and cortisol secretion. Endocrinology 96:1088, 1975.